Micro-organism inactivation system

ABSTRACT

A portable micro-organism inactivation system comprising: a casing mounting, a UV radiation source, a pump, and releasable tube support for supporting an elongate tube to define a flow path extending therethrough which is substantially free of substantial discontinuities are provided by the present invention. The elongate tube has a first portion and a second portion wherein the first portion has a UV-transparent wall. The first portion extends in close proximity to the UV radiation source within an irradiation zone thereof while the second portion is interfaced with the pump for pumping of fluid through the system so that substantially the whole of said individual fluid unit is exposed to a similar micro-organism inactivating level of UV-irradiation, while minimizing damage to the desired components thereof. The invention also provides a method of micro-organism inactivation in a fluid using a system of the invention.

The present invention relates to a method of and apparatus for theinactivation of microorganisms in blood and blood products using lightradiation and continuous flow and able to operate on individual plasmadonations or small volume blood products.

Removal or inactivation of microorganisms (especially viruses andbacteria) from blood and blood products is increasingly required toensure the highest standards of safety and product quality. The labilityof many blood components, cells and proteins severely limits, however,the more stringent treatments normally applied to sterilize fluids.Various treatments have been used in blood and blood products processinglaboratories such as filtration, heat, and X- and gamma ray radiation,organic solvents and detergents. Heat and radiation treatments however,usually require stabilizer to be added and later removed. Solvent anddetergent processing also require removal of these materials. It isgenerally desirable to avoid adding or removing substances to blood orblood products. Existing procedures currently in place for treatingblood products moreover only inactivate a proportion of virus types, forinstance some viruses are extremely heat resistant and others are devoidof membranes and thus resist solvent-detergent treatment. Such virusescould be removed by filtration if they were large enough, butunfortunately the heat-stable and non-enveloped viruses such asparvovirus and hepatitis are too small to be effectively removed byfiltration. An additional problem is that unknown viruses will alsoexist, and an ideal inactivation method should inactivate these as well.Currently regulatory authorities require a combination of two differentinactivation techniques to be applied, which should be orthogonal orbased on independent physico chemical principles.

In principle, light (especially ultraviolet light) would be an excellentchoice as it adds nothing, is orthogonal to existing methods (such asheat, solvent-detergent, filtration and γ-radiation) and has beensuccessfully used for some time in both air, surface and watersterilization. Unfortunately the use thereof when applied to fluids suchas blood and blood products has been frustrated by the high degree oflight adsorption thereof. Many blood products strongly adsorb light andultra-violet light even more so, due to the presence of haemoglobin andplasma proteins in high concentration. The primary result of this isthat light penetrates only a very short distance into the fluid and thebulk of it is shielded from any germicidal action. In the case ofultraviolet light, for example UV-C or 254 nm wavelength light asemitted by the common low pressure mercury discharge lamp, the depth ofpenetration (defined as the point where the light intensity has beenreduced to one tenth of its initial value) into blood products such asalbumin and immunoglobulin solutions will vary depending on the proteinconcentration from about 1.0 mm down to as little as 0.05 mm. Thus themajority of UV light applications to blood products have tried to solvethis problem by working with thin films of solution much less than 1 mmthick. Limited success has been reported, either because the process isinsufficiently effective, and viruses survive to transmit diseases,and/or because the labile blood factors are inactivated and the productis not useful. More recently, efforts have been made to identifychemical additives which can be used to synergise the effect of light(by enhancing its microbial killing power) and/or other additives havebeen identified which reduce the damage caused to labile blood factorswithout also reducing the microbial killing effect. A problem is thatmany of these additives are toxic, and need to be removed aftertreatment. Unfortunately no reliable methods exist to treat plasma so asto inactivate all known viruses, let alone unknown viruses, whilstleaving the labile factors intact and functional. Due to theparticularly stringent safety requirements applicable to blood and bloodproducts, and the relatively cumbersome and complex nature of thesterilization procedures currently in use, as far as we are aware, therehas been no serious consideration by anyone else of the possibility ofachieving effective sterilization of such fluids outside the laboratory.Also, due to the relatively large scale of apparatus in use in blood andblood products processing laboratories, it has not been practicable tosterilize small quantities of such fluids such as single unitcontributions in volumes of typically 250 to 500 mls, which may berequired in the case of rare blood types, or particularly specializedproducts. Neither has there been any system available for rapid reliablesterilization of such small quantities of blood or blood products suchas plasma out in the field more or less directly after collection ofblood from a donor.

In more detail, conventional processing methods for virus inactivationin plasma and blood products usually require significant volumes ofpooled product to be feasible for processing on an industrial scale. Theuse of such industrial scale equipment for processing of singledonations of plasma or small pools of blood products (such as specificimmunoglobulins) is not feasible, as the losses involved can beconsiderable. For example, a single donation of plasma from anindividual donor typically has a volume of 250 ml and a double donationof plasma from an individual donor (eg obtained by plasmapheresis) willstill only have a volume of about 500 ml. These volumes are of the sameorder of magnitude as the void volumes in industrial process scaleequipment and substantial losses would accordingly be inevitable.Similarly, pools of specific antibodies for highly specializedapplications (such as anti-rabies, anti-tetanus, anti-zoster andanti-rhesus) can range in volume from as little as 1L up to just a fewtens of litres, again making them impractical for processing in largescale virus inactivation equipment.

Our own earlier European Patent No. 0 422 007 B discloses a relativelycompact apparatus for sterilization of small quantities of blood orblood products inside a generally cylindrical bag or vessel by rollingit during irradiation thereof. The facilities for controlling theevenness of the radiation dosage applied throughout the fluid andminimizing damage from localized overheating and/or over-irradiation,are, however, somewhat limited.

It is an object of the present invention to avoid or minimize one ormore of the above problems or disadvantages. It is a further object ofthe invention to provide an apparatus and method whereby microorganisminactivation without loss of product activity can be achieved withoutthe need for adding or removing anything.

The present invention is based on our detailed investigations into theuse of highly efficient mixing to overcome the twin problems ofmaximizing microorganism inactivation whilst minimizing product damage.An illuminated but intensely adsorbing fluid flowing in a pipe can beconsidered as having a thin “killing zone” at the outer surface ofvariable thickness and a major lumen occupying the remaining centralvolume which is not illuminated and therefore allows any microorganisme.g. virus to be preserved intact. By efficiently transporting fluidfrom the central “dark” zone to the outer “killing zone” and back again,a sufficiently large number of times and in a reliable and predictablemanner, it should be possible to ensure that no virus escapes receivinga dose of illumination and that such dosing is uniform for all particleswithin the fluid. Since viruses are very small (≧20 nm) compared to thedimensions of a pipe it is easy for them to escape being uniformlyirradiated and thus any mixing system has to be extraordinarilyefficient at the microscopic level. We have found that static mixerscan, but only when operated under certain clearly specified conditions,deliver such reliable and predictable performance. Such static mixersgenerally comprise a series of alternating left and right handed helicalelements which divert the fluid flow left and right alternately andcontinuously re-divide the fluid differently into two halves. Suchdividing operations can be repeated ‘n’ times by assembling a series of‘n’ mixers in sequence such that the total number of subdivided volumeelements is given by the expression 2^(n). This apparently simpleapproach can lead to astronomically large numbers of subdivided volumeelements, eg. with 266 mixers one can obtain 10⁸⁰ subdivided volumeelements. Such a mixing system is convenient and reliable because it hasno moving parts (other than the process fluid) and for labile biologicalfluids such as blood and plasma it minimizes the chances of damagecaused by shear, heating or mechanical strain. Surprisingly, though, wehave found that increasing the number of mixing elements per se is notsufficient by itself, reliably to inactivate virus in a predictablemanner. Specifically, increasing the time a virus spends in theilluminated device will often not lead to a proportionate increase inthe amount of virus killing. Instead, a residual amount of viruspersists no matter how long the exposure time. This is a seriousproblem, (and is common to many different inactivation methods) as itnot only makes the virus kill hard to predict but residual infectivevirus can be a serious liability in any blood product. Thus ideally onewould seek to have a linear increase in virus kill with exposure time orlight energy dose. It might be thought that increasing the intensity ofthe light source would be a solution to this problem. However such anapproach has to date not been successful, and calculations based on thedegree of penetration of light in strongly adsorbing fluids show thatwith eg. a “killing zone” of 0.05 mm thickness in a pipe of 20 mmdiameter would require an increase in light intensity of 200 fold toilluminate the centre of the fluid lumen within the pipe. Such a sourceis not readily available and an additional problem with this approach isthe increased risk of damage to labile molecules caused by the intenseradiation at the surface of fluid and overheating. Surprisingly, we havefound that it is possible to use low power light sources and stillachieve good virus kills provided the mixing elements are operatedwithin a clearly defined efficient flow regime. We have recentlydeveloped pilot and process scale devices (unpublished patentapplication PCT/GB99/03082) operating with pipes in the 4–25 mm diameterrange. These are suited to treating pooled or manufactured bloodproducts typically in the range of 1 L to 10,000 L, but because of theirdead volume they are not suitable to treating individual donations ofblood or plasma prior to pooling. Such donations typically have volumesin the range from less than 100 to 1000 ml or thereabouts and have nothitherto been amenable to any practical form of virus inactivation whichis universally active against all viruses (It should be noted that thevisible light methylene blue combination process marketed by Baxterunder the trade name “PathInact” is only efficient against envelopedviruses).

Surprisingly, we have found that, depending on the fluid velocity orflow rate through the optical mixer device, there exist two distinctmodes of operation: one which we describe as “efficient mixing” whichexists above a certain fluid velocity or flow rate and the other whichwe describe as “inefficient mixing” which obtains below this velocity orflow rate. The transition from one to the other mixing regime occursover a quite small range of fluid velocity or flow rate and can bepre-determined for a given combination of mixer diameter, tube lengthand feedstock fluid. Once determined, this efficient mixing regime canbe reliably used to predict virus kill as a function of machineparameters and feedstock properties and this is a valuable property invalidating a process or machine for the production of safe bloodproducts. Surprisingly, we also find that as the fluid velocity or flowrate increases, the efficiency of virus inactivation (expressed as logskill per second of exposure) is maintained constant or even increasedwhilst the degree of damage, (expressed as residual clotting factoractivity recovered in plasma) decreases. Thus, unexpectedly, the controlof flow rate not only improves the predictability of virus kill and theefficiency of virus kill but it also reduces the amount of productdamage. This is a most valuable and surprising result, since bloodproducts which are quite labile can now be subjected to efficient virusinactivation without the need for additives, and more specifically it isnow possible to treat individual blood and plasma donations in a waythat will significantly reduce the risk of disease transmission by knownor unknown viruses. By this means we have found it possible to providean apparatus with fluid pipes in the size range 1 to 4 mm id containingstatic mixers in an UV-irradiation zone which can be used for theeffective treatment of individual donations of blood or plasma and smallvolumes of blood products in the range 100–1,000 ml. Thus the presentinvention provides a portable micro-organism inactivation systemsuitable for use with individual fluid units, comprising:

-   -   a casing mounting a UV radiation source, pump means, and        releasable tube support means; and    -   an elongate tube having:    -   a first portion with wall means of a UV-transparent material,        and having an internal diameter of up to 4 mm, generally from        0.1 to 4 mm, preferably, from 1 to 4 mm, and containing a static        flow mixing means extending therealong with a multiplicity of        mixer elements for repeatedly subjecting a fluid flow        therethrough, in use of the device, to a mixing operation        comprising dividing and remixing of the fluid flow, in use of        the system,    -   a second portion interfaced with said pump means for pumping of        fluid therethrough by said pump means in use of the system,        upstream and downstream ends provided with first and second        coupling means respectively for releasable fluid-tight        connection of said elongate tube, in use of the system, to an        individual fluid unit container of fluid to be treated and to a        treated fluid container for receiving treated fluid,        respectively, and having a sterile interior,    -   said releasable tube support means being formed and arranged for        releasably supporting said elongate tube so as to define a flow        path extending therethrough which is substantially free of        substantial discontinuities so as to avoid substantially        turbulence in fluid flowing therealong in use of the apparatus,        and with substantially only said first portion extending in        close proximity to said UV radiation source within an        irradiation zone thereof, and with said second portion        interfaced with said pump means,    -   whereby in use of the system substantially the whole of said        individual fluid unit may be exposed to a similar micro-organism        inactivating level of UV-irradiation, whilst minimizing damage        to the desired components thereof, and then collected in a said        treated fluid container.

In another aspect the present invention provides a method ofinactivating micro-organisms in an individual fluid unit comprising thesteps of:

-   -   providing an apparatus of the invention;    -   coupling an individual fluid unit container containing a said        individual fluid unit and a container having a sterile interior        for receiving treated fluid, to the upstream and downstream ends        of the elongate tube; and    -   pumping said fluid from said individual unit fluid container        through said elongate tube into said container for receiving        treated fluid while irradiating the first portion of said tube        with said UV-radiation source.

Preferably the method of the invention includes the preliminary step ofmounting a previously unused said elongate tube in said releasable tubesupport means.

It is also possible to use the present invention for the sterilisationof blood or blood products substantially directly following collectionthereof from a donor. Thus an irradiation apparatus of the invention maybe used in combination with a blood or blood product donation collectionapparatus without the need for collection in a bag before sterilization,the donation being collected directly into a treated fluid bag or othercontainer downstream of the inactivated tube first portion.Alternatively the irradiation apparatus could be used in combinationwith a plasmapheresis apparatus for sterilisation of the plasmaextracted from a blood donation, prior to return of the donation residue(usually comprising primarily red blood cells) is returned to the bodyof the donor. It will of course be appreciated that where the donationcollection apparatus itself normally includes a pump means, then one orother of the donation collection apparatus and inactivation apparatuspumps would normally be omitted. Where the latter pump is the oneomitted, it would of course be necessary for the former to beconfigurable to provide a flow rate in the efficient mixing zonerequired by the present invention. Thus in a further aspect the presentinvention provides a method of obtaining a sterilized blood or bloodproduct donation from a donor which method comprises the steps of:

-   -   providing a blood or blood product donation collection apparatus        having a sterile, blood or blood product receiving, container,        and a microorganism inactivating apparatus of the present        invention;    -   coupling the upstream and downstream ends of the elongate tube        of the microorganisms inactivating apparatus in-line with the        blood or blood product donation device upstream of said blood or        blood product receiving container; and    -   pumping said fluid from the donor through said elongate tube        into said, blood or blood product receiving, container while        irradiating the first portion of said tube with said UV        irradiation source.

It should also be noted that the methods and apparatus of the presentinvention are also useful for the sterilisation of a wider range offluids which may require treatment in relatively small volumes outsideof dedicated sterilisation plant. Such fluids may on the one handinclude blood or blood product obtained from transgenic animals, otherbiological fluids obtained using biotechnological procedures such asgenetic engineering, and on the other hand cutting fluids used inmachine tools such as lathes etc for drilling, milling, cutting and likeoperations, and the present invention encompasses the application of thenovel methods and apparatus disclosed herein, to these also.

Thus by means of the present invention it is possible to achieve highrates of microorganism inactivation with minimal product damage on smallvolumes of blood or blood products, in a simple and economic matteroutside of dedicated processing laboratories. It is a further advantageof the present invention that products which have hitherto not beenamenable to virus inactivation can now be processed with minimalvolumetric losses, for example the void volume in the system andapparatus of the present invention can be as little as 1–10 ml whichreduces volumetric losses to the order of a few percent or less in thecase of small quantities of fluid. Yet another advantage of the proposeddevice and process is that the costs associated with the processing stepand equipment are minimal, making it feasible to process raw materialsuch as plasma in single or double donation volumes without major addedcost. The light source and pump use power of only a few watts and theilluminated mixer element is sufficiently small and composed of massproduced plastic items (which are readily assembled by eg a heatshrinking step) to permit them to be used once only and disposed ofafter use. Furthermore, the disposable element contains no sharp metalor glass components which makes it safe to dispose of even when incontact with potentially infectious material. It is a further advantageof this device that, following use, the disposable element will havebeen sterilized, thus further reducing risks of infection.

Various pump means may be used in accordance with the present invention.In order to minimize the risks of contamination there is preferably useda pump of a type in which the pump motor and drive transmissioncomponents are isolated from the fluid. Thus for example, there may beused a diaphragm pump in which the second portion of the tube isconnected via one-way inlet and outlet valves to a chamber having adiaphragm wall portion which is reciprocably displaceable by a pumpmotor and reciprocating drive output member inter engaged with theoutside of the diaphragm wall. In this arrangement only the interior ofthe chamber and the valves need to be sterile. Most conveniently thoughthere is used a peristaltic pump in which a rotary drive output memberwith a series of circumferentially distributed transverse rollers orbars is used to repeatedly apply a constriction to a length of the tubecorresponding to the second portion thereof which constriction advancesalong the length of said second tube portion wherein the pump motor anddrive transmission components are entirely isolated from the fluid flowthrough the second portion of the tube which can be integrally formedwith other parts of the elongate tube. This simplifies replacement ofthe tube after each use of the apparatus and minimizes the number ofcomponents requiring to be replaced after each use. Nevertheless it willbe appreciated that other kinds of pumps could in principle be usedprovided that all fluid-contacting surfaces are sterile, the design offluid flow passages and fluid flow impeller means is such as tosubstantially avoid turbulence in the fluid flow, and the cost of thepump (or relevant components thereof) permits disposability thereofafter a single use.

As noted hereinabove we have found that by suitable control of the fluidflow rate through the first portion of the tube, it is possible toachieve high rates of microorganism inactivation whilst minimizingdamage to the desired components of the fluid. Thus in a particularlypreferred aspect of the present invention, the pump means is formed andarranged so as to provide a fluid flow rate at a fluid flow rate notless than a minimum flow rate corresponding to a maximum fluid residencetime (within said irradiation area) required for efficient mixing asindicated by the maintenance of a substantially linear relation betweenlog kill and residence time which obtains above said minimum flow rateand at a fluid flow rate not greater than a maximum fluid flow ratecorresponding to a minimum residence time in said irradiation arearequired for effective inactivation of a said contaminatingmicro-organism by providing a desired log kill of said micro-organism,(preferably not less than that required for a 4 log kill of saidcontaminating micro-organism, in general not less than 1 second, forexample, not less than 10 seconds), wherein said minimum residence timein said irradiation area is defined in accordance with the followingrelationship:log 10 kill=K×Flux×Residence time/OD×Tube Radiuswherein Flux indicates the amount of UV radiation incident on thepassage containing the fluid flow in the irradiation area, in mW cm⁻²;OD is the Optical Density (absorbance of 1 cm) of the fluid at thewavelength in the region where substantial virus inactivation takesplace (typically in the range 250 to 280 μm); K is an empiricallyderived constant; and Tube Radius is the internal radius of the vesselin the irradiation area, in cms,

-   -   whereby in use of the apparatus substantially the whole of the        fluid may be exposed to a similar micro-organism inactivating        level of UV-irradiation whilst minimizing damage to the desired        component(s) of the fluid.

It will be appreciated that this is a modified form of the Bunsen-Roscoereciprocity law, derived for microbial killing on a surface, whichstates that LRV=constant×light flux×exposure time. The additional termsneeded to cope with a flowing fluid in a thick adsorbing layer are theoptical density of the process fluid and the pipe radius. This “ideal”relationship predicts a linear dependence of virus kill on residencetime and this is only true in the “efficient mixing” zone indicated (fora particular case) in FIG. 3, in which zone log kill is linearly relatedto residence time. At flow rates of less than a defined amount, themixing becomes inefficient and the above simple relationship does notobtain. Thus it is necessary to operate in the “efficient mixing” regimein order to be able to predict the virus kill in response to equipmentand process variables. The value of the composite constant K is mosteasily determined empirically for a model virus such as bacteriophageØ×174. Once this value is determined, the value can be estimated forother viruses using the published absolute/relative values for othermicroorganisms relative to bacteriophage Ø×174. The value of theeffective lamp power (Flux) is most easily determined by actinometryusing the below described actinometry system.

The elongate tube may be a simple continuous length of tube having theUV-transmissibility required for the first portion thereof and thephysical characteristics e.g. flexibility required of the second portionfor effective interfacing with a suitable pump drive mechanism such as,for example, a peristaltic pump. More commonly though the elongate tubemay be made of discrete sections of different materials with differentproperties optimized to a greater or lesser extent for the respectiverequirements of the first and second portions, and one or more connectorsections used for interconnecting these to each other (albeit that oneor more of these connector sections and/or the coupling means may beformed integrally with one or other of the first and second tubeportions).

The first portion of the tube has an internal diameter of up to 4 mm andpreferably has a series of helical static mixer elements disposed withinthe lumen. Advantageously there is used a static flow mixing means inthe form of an elongate screw threaded member having alternate mixerelements of opposite handed screw thread. Static flow mixers of thiskind have been known and used for many years for various purposes suchas food and chemical product manufacture, and are commercially availablefrom inter alia Chemineer Inc of North Andover, Mass., USA under theTrade Name KENICS KM and Liquid Control Ltd of Wellingborough, Englandunder the Trade name POSIMIXER, and provide very intensive mixing as aresult of a combination of a number different mixing effects comprisingflow division through repeated division of previously divided streamsthus creating a geometric progression of flow division according to theformula D=2n where D is the number of flow divisions and n is the numberof mixer elements; flow reversal whereby the direction of rotation aboutthe longitudinal axis of the mixer is reversed at each mixer element(clockwise—anti-clockwise—clockwise etc.); radial mixing resulting fromflow reversal and flow inversion which occurs when fluid close to thecentre of each of the separate flows at a mixer element of the device isdriven radially outwardly when it encounters the edge of a new mixerelement; and resulting inhibition of axial differentiation(corresponding to establishment of axial flow profiles).

The first portion of the tube is positioned close to the surface of aUV-radiation source, preferably one emitting UV-C radiation, such as alow pressure mercury discharge lamp emitting light energy primarily inthe 254 nm line. The material of the tube is generally chosen so that ithas a reasonable transmissibility to 254 nm radiation. Suitablecommercially available materials typically transmit 50 to 85% of suchradiation. The thickness of the tube wall can also be varied and chosenfor a given material so as to be in this range of transmission, eg. a 1mm thick wall silica tube or a 0.2 mm thick wall pTFE tube. The lengthof the first portion of the tube is conveniently chosen to approximatelycorrespond to the length of the UV-radiation source. Various suitable UVlamp sources may be used in the system and apparatus of the presentinvention. In general it is preferred to use a relatively compact lowpower UV source. In the case of a Phillips PLS 11W TUV lamp the lengthis 19 cm whereas for a Phillips 15W TUV lamp this is 45 cm. More thanone length of tube can be disposed in the irradiation zone adjacent theUV-radiation source lamp so that the first portion comprises a pluralityof lengths of substantially UV transparent tubing containing staticmixer elements, which lengths are inter connected in series by flexibleor rigid connecting sections which need not be necessarily UVtransparent.

By using relatively small low power UV radiation sources, it is possibleto use portable power sources such as batteries, convenientlyrechargeable batteries and/or solar cells, manually driven dynamos,conveniently with coiled spring, flywheel etc energy storage devices.Such means enhance still further the portability and in-the-fieldcapability of the system and apparatus which make it particularlysuitable for emergency, disaster relief, and like applications.Nevertheless the UV radiation sources and pump means may also be ofmains powered type for applications where mains electricity is availableand/or for use together with portable generators.

The “efficient mixing”regime and the minimum desirable flow rate may bereadily determined by means of simple experimental procedures as furtherdescribed hereinbelow. A quantity of fluid of the type requiring to betreated, spiked with a marker virus (eg. bacteriophage Ø×174) to a hightitre (typically 1:10⁸) is pumped through a given diameter and length ofthe tube first position while it is being irradiated. The flow rate isvaried from a low value eg. 2 ml/min to a high value eg. 100 ml/minusing suitable flow rates in between these limits. Samples of irradiatedfeedstock are collected for each flow rate and the degree of virusinactivation is plotted against the residence time (Rt) of particlewithin the mixed illuminated zone. The value of Rt is most easilyderived by measuring flow rate and dividing by the predetermined mixedilluminated void volume. When plotted in this way a characteristic shapeof curve is obtained (see FIG. 3), figures in parentheses indicate theflow rate in ml/min at each data point. For shorter residence times(i.e. for faster flow rates), the amount of virus kill increaseslinearly from the origin and rises steeply, however at a certain narrowrange of flow rate (residence time) the virus kill ceases to increaseand the amount of residual surviving virus remains constant despiteincreasing residence time (and hence increasing doses of radiation). Theinitial (steep) slope of the curve represents the region of “efficientmixing” whereas the later flat part of the curve represents the regionof “inefficient” mixing. The transition between the two indicates theflow rate below which the device should not be operated with thatfeedstock and that tube-static mixer combination. This observation hasseveral important and valuable implications. Firstly, it is clear thatto scale-up the dose of radiation it is generally better to increase thelength of pipe (or use multiple passes) rather than to decrease the flowrate (and increase the residence time). Secondly, once a particularfeedstock and mixer element size has been chosen, a minimum flow ratefor this combination must always be respected to achieve high efficiencyof virus inactivation. Thirdly, because the steeper part of the curve issubstantially linear, it allows for more reliable prediction of viruskill when changing process parameters such as OD, flow rate, lamp power,number of lamps, pipe material and thickness, and pipe length anddiameter e.g. in order to easily accommodate variations in OD betweenindividual donations and also allows for more reliable design ofapparatus to yield a given target level of virus inactivation. An addedadvantage of operating in the “efficient mixing” region is that itminimizes damage to labile components at the surface of the tube causedby over-exposure to excessive radiation and minimizes local overheatingby efficient and rapid transport of heat away from the tube wall andinto the cooler bulk of the fluid.

Once the minimum flow rate is known, the desired virus kill can beachieved by either increasing the length of optical mixer pipe and/or bypassing the fluid through the device several times. Scaling up thelength of pipe is primarily limited only by the back pressure caused bythe number of mixer elements and the viscosity of the feedstock. Whenthe back pressure exceeds the desirable limit set by the pump, tubingand connectors, then greater virus kill can still be obtained by usingthe multiple pass strategy, ie the batch of fluid to be processed can bepassed through more than once. Generally however, as plasma has quite alow viscosity there may be used a tube length such that a single pass issufficient to give adequate virus inactivation and this is very muchpreferred in view of greater ease and simplicity of operation andgreater safety and reliability.

The degree of labile plasma factor damage can be estimated by assayingfor individual coagulation factors using assays, well known to thoseskilled in the art. Such factors include fibrinogen, factor V, factorVIII, factor IX, factor X and factor XI. The extent of retention ofthese factors for different degrees of exposure to radiation can be usedto set an upper limit for the amount or radiation dose (fluence ormJ/cm²) that is acceptable. (Where the flux of the lamp is known inmW/cm², the fluence, or work done per unit area of the device can becalculated by multiplying the residence time in seconds and the lampflux, the units of fluence are thus mJ/cm². In many cases, it is morerealistic to calculate the work done on the process fluid as Joules perml of product. To convert from fluence (in mJ/cm²) into Joules/ml afactor of 2/r is used where ‘r’ is the pipe radius in cm, a factor of1/1000 is used to convert mJ into Joules, and a correction factor kA/Vis also required to convert for the proportions of surface area andvolume occluded by the presence of the mixer elements within the pipe.This factor is typically 1.275 for the case of a 3 mm static mixer ofpreferred type described hereinbefore. Thus the overall conversionfactor is 2/r× 1/1000×1.275 =0.017). Surprisingly, we have found thatdamage to labile factors can be minimized by operating at or above theminimum flow rate for “efficient mixing” and that additives are notrequired to protect the labile factors from radiation damage.(Nevertheless if it is required to employ an additive for some reason,this can also be done without departing from the scope of the presentinvention, albeit that this is less preferred). A likely mechanism forthis self-protection is that “hot spots” at the wall of the tube areminimized and no molecule is subjected to any greater dose of radiationthan any other. Thus, operation in the region of “efficient mixing”simultaneously enhances virus kill and minimizes protein damage—probablyby the same mechanism of extremely uniform mixing at the microscopiclevel.

It is often desirable to measure the actual dose of light energyadsorbed by a flowing fluid within the lumen of the optical elements.Although this can be estimated from the known power of the lamp and theresidence time in the device a number of confounding factors seriouslylimit the accuracy of this approach including heterogeneous distributionof light, variable transmission of the wall of the optical element pipeand scattering and reflections. Thus a more direct approach isdesirable, however it is not feasible to place electronic sensors withinthe lumen of the small pipe diameters used, nor do they accuratelyreproduce the extremely heterogeneous nature of the adsorption processcaused by self adsorption of the feedstock.

We have found that appropriately formulated sodium iodide can be usefulas an actinometric reagent to measure the absolute and relative amountsof light-work done on the process fluid. Such a reagent typicallyconsists of 1% w/v NaI in 20 mM Tris buffer pH 7.50+0.01. The accurateadjustment of pH is important as this controls the sensitivity of thereagent. At acid pH values the reagent becomes more sensitive and atalkaline pH values it becomes less sensitive. The reagent can be storedfor several weeks at 20° C. in a dark cupboard. In order to provideabsolute units (J/cm³) of work done by light energy adsorbed per unitvolume of process fluid, the reagent was placed in a 10×10 mm crosssection silica cuvette at a distance of 50 mm from a source of UV-C andat the same distance an integrating UV-C electronic power sensor wasalso positioned. The reagent was stirred vigorously with a magneticstirrer whilst illuminated with UV-C light for varying periods of time.The visible yellow colour due to iodine formation was quantitated byspectrophotometry in a 1 cm path length cuvette at 352 nm and plottedagainst the integrated value of the meter display in mJ/cm². For a 1 cmsquare cross section cuvette, the numerical value of mJ/cm² is the sameas that value in mJ/cm³ because 1 cm² of surface area corresponds to1.00 ml of solution. The results of this absolute calibration curve areplotted in FIG. 4. If relative rather than absolute comparisons of workdone on the process fluid are adequate, eg. to validate that theequipment is delivering the same light dose on successive occasions,then it is feasible to just quote the absorbance value A1 cm obtainedwith the actinometry reagent when pumped through the device at the sameflow rate as the process feedstock. For a given lamp/pipe combination,it is possible to work backwards from the observed actinometryabsorbance values, the interpolated work density (in J/ml) and theresidence time (Rt) to derive an apparent or effective lamp power inmW/cm², which can be useful in monitoring lamp performance or designingnew equipment to give a particular numerical value of virus kill. Inparticular a knowledge of the effective lamp power in absolute units ishighly desirable to insert into an equation for calculating orpredicting virus kill. Such an absolute value of the effective lamppower cannot be measured directly by electronic sensors because of theabove mentioned confounding factors (heterogeneity, transmission losses,reflection and refraction). An additional advantage of the iodide basedactinometric reagent is its insensitivity to visible and near UV light(the absorption of the reagent is essentially nil above a wavelength of300 nm) in contrast the reagent adsorbs strongly at 254 nm., having anabsorbance A1 cm of about 20 AU, and in this respect it is a usefulanalogue of any strongly adsorbing process fluid, mimicking the stronglyheterogeneous adsorption process in a thin layer at the surface of theoptical pipe.

Further preferred features and advantages of the present invention willappear from the following detailed description given by way of exampleof a preferred embodiment illustrated with reference to the accompanyingdrawings, and from the following examples of the use and calibration ofthis embodiment.

In the drawings:

FIG. 1 is a schematic side elevation of an irradiation system of theinvention (with the first portion of the tube shown displaced forgreater clarity);

FIG. 2 is a detail cross-sectional view of the system of FIG. 1; and

FIGS. 3 to 6 are graphs of the measurements obtained in the followingexamples.

FIG. 1 shows an irradiation system of the invention 1 comprising acasing 2 (see FIG. 2) having a plurality of tube support clips 3 (onlysome shown) for releasably securing an elongate tube 4 having a firstportion 5 including two lengths of UV transparent tubing 6 containingstatic mixer elements 7, and a second portion 8 supported in engagementwith a peristaltic pump device 9. (Note—the two lengths of UVtransparent tubing 6 are actually disposed as shown in FIG. 2 so as tomaximize the UV radiation dosage incident thereupon and have been drawnout of position in FIG. 1 solely for the purposes of greater clarity).In more detail a series of eight 3 mm diameter static helical mixermouldings (MeterMix Company of wellingborough, England Part No: MM0308)having a total assembled length of 190 mm was mounted within a length ofheat shrinkable PTFE tubing 6 (Adtech Part No: FHS 2.7), wall thickness0.2 mm; ID before shrinking 3.6 mm; ID after shrinking 3.0 mm, toprovide the first tube portion 5. The actual length of tubing aftershrinking was 265 mm which allows for connections at either end outwitha central irradiated mixing portion. Each mixer element mouldingconsists of 8 individual helical elements, giving a total of 64 binarymixing/dividing elements or 2⁶⁴ subdivided volume elements ie. 1.8×10¹⁹.The internal mixed irradiated volume (Vo) was determined to be 0.94 mlby injecting water and weighing. The characteristic dimension of thefinal subdivided volume element is thus defined as ³√Vo/2⁶⁴ or³√0.94/1.8×10 ¹⁹=4×10⁷ cm or 4×10⁻⁹ m or 4 nm, which is significantlysmaller than the target viruses of 20 nm diameter.

This first tube portion 5 is mounted using release tube support clips 3in close proximity to a UV source 10 in the form of a PhillipsPLS11W-TUV low pressure mercury discharge lamp which consists of twolamp tubes 11 joined together in a ‘U’-shaped format with a centralgroove at either side which provide convenient mounting positions forthe first portion parallel to the lamp tubes. The length of the lamp is190 mm which dictates the irradiated length of the first tube portionsections 6. (The effective length of the irradiated first portion beingapproximately 2×190 mm). The upstream and downstream ends 12 of thefirst tube portion 5 are conveniently provided with male or female Luertype fittings 13 which allow ready connections to existing medical gradesterile tubing, transfer packs, pump elements etc. Other suitable modesof sterile connecting device will be apparent to those skilled in theart. A Gilson Minipuls III pump (available from Anachem company ofLuton, England); having a flow rate adjustable within the range from 1to 100 mls/min (for a tube i.d. of around 3 mm) engaging a 3 mm i.d.tube second portion, is conveniently used as the peristaltic pump 9.Conveniently also temperature sensing probes 14 are provided at theinlet and outlet ends 12 of the first portion and a pressure sensor 15at the outlet 16 of the pump 9 for the purposes of monitoring theoperation of the system in the course of establishing its performanceparameters although these would not be necessary during normal use ofthe apparatus. The second portion 8 of the tube 4 was a flexiblematerial such as Marprene (Trade Name) (available from Watson-Marlow ofFalmouth, England) commonly used in peristaltic pumping situations. Itwill of course be appreciated that for a single-use application such asis contemplated by the present invention, a tube material withsignificantly shorter wear life—such as silicone, polyurethane, or PVC,would be quite acceptable. A first bag 17 containing freshly collectedplasma 18 is connected using a Luer type coupling 19 provided at theupstream end 20 of the tube 4, and a sterile second bag 21 for receivingthe sterilized plasma 22 was connected in similar manner using a Luercoupling 23 at the downstream end 24 of the tube 4. Once the contents 18of the first bag 17 had been processed the second bag 21 containing thesterilized plasma 22 is detached from the tube 4 and sealed. In normaluse the complete tube 4 is then removed from the releasable clips 3together with the first bag 17 for safe disposal, and a fresh tube 4mounted in position and a new bag of plasma requiring treatment may thenbe connected thereto, along with a fresh sterile bag for collection ofsterilized plasma.

EXAMPLE 1 Measurement of Damage to Plasma Components, and ActinometryMeasurement

Bags of plasma (150 mls) were connected to the upstream end of theelongate tube of an apparatus as illustrated in FIGS. 1 and 2 but with asingle UV transparent tube length 6 in the first tube portion 5. Plasmawas pumped through the apparatus at various flow rates and thetemperature rise of the feedstock, back pressure and flow rate weremonitored. Samples of plasma at each flow rate were collected andsubsequently analyzed for fibrinogen and coagulation factors V, VIII,IX, X and XI. After flushing with saline to clean the device, an iodidebased actinometric reagent as described hereinbefore was pumped throughthe device at the same pump settings and the absorbance values A1 cmwere determined after holding the samples for 1 to 2 hours. The physicalvalues obtained are summarized in Table 1 and the biological assayvalues are summarized in table 2 From table 1 it will be seen that themaximum temperature rise seen was 20° C. at a residence time of 28.1seconds. Therefore assuming a feedstock input temperature of 20° C.,this would raise the product to 40° C. which might be considered toohigh for labile coagulation factors, so a residence time of 14.3seconds, giving a temperature rise of 14.7° C. and a final producttemperature of 35° C. would be acceptable, being within thephysiological range. The pressure drop ranged from 1.3 to 3.76 psi whichis low and comfortably within the limits for conventional peristalticpumps and tubing connectors. The actinometry absorbance values show asmooth increase with exposure time, and can be interpolated in acalibration curve (see FIG. 4) to provide absolute values of theirradiation energy level in Joules/ml and by means of a constant for theapparatus, mentioned above, can be converted into fluence or mJ/cm^2values. Both these sets of data can in turn be used to calculate theapparent lamp power (via the individual values of the residence time),which in this case is approximately 16 mW/cm{circumflex over (2)}.

The bioassay data in table 2 show that plasma coagulation factors havevarying susceptibility to UV-C induced damage.

The sequence of increasing sensitivity to damage was factor V<factorVIII<fibrinogen<factor IX<factor XI. Thus factor XI would appear to bethe most sensitive indicator of damage, and if a practical limitof >/=0.70 international units per ml of product were desired, then theconditions of using pump setting P3 should not be exceeded (ie aresidence time of 5.81 seconds or fluence of 165 mJ/cm^2). Under theseconditions, the yield (undamaged) of other factors would then be factorV 88%, factor VIII 84%, fibrinogen 77%, and factor IX 74%.

EXAMPLE 2 Inactivation of Virus in Plasma

The procedure as described in example 1 was again used, except that theplasma feedstock was spiked with the bacteriophage virus Phi-X 174 to atitre of 1:10^8, and the plasma was pumped through the device at flowrates ranging from 2 ml/min to 20 ml/min. The optical density (OD) ofthe feedstock was measured (after diluting ten-fold for measurementpurposes) and was calculated back to be 23.38 AU at 254 nm in a 1 cmcuvette. The titre of the virus in the irradiated plasma was determinedby serial dilution on bacterial plates of E. coli and the decrease inlog titre was calculated to quantitate the value of the LRV (logreduction value). The various measurements recorded are summarized inTable 3 and are in general rather similar to the data in Table 1. Thevirus kill (last column of table 3) was plotted against the residencetime (third column of table 3) in FIG. 3, the figures in parentheses ateach point plotted being the flow rate for that measurement. Plottinglog kill against flow rate is less informative than plotting againstresidence time. The latter plot clearly shows (FIG. 3) that at flowrates above 8 ml/min the slope of the virus kill versus residence timeis 0.45 log kill units per second whilst at flow rates below 6 ml/minthe kill is much less efficient with a slope of only 0.04 log kill unitsper second, ie a reduction in efficiency of around ten fold. From thedata of table 3 and FIG. 3 we conclude that it is necessary to operateabove a minimum flow rate which can be deduced experimentally for aparticular mixer diameter and feedstock composition from a plot of logkill versus residence time.

EXAMPLE 3 Inactivation of Virus Using Increased Irradiation Flow PathLength

The procedure as described in example 1 was followed except that twolengths of UV transparent tube were placed at opposite sides of thelight source and connected in series such that the mixed irradiated pathhad a total length of 380 mm with 16 moulded mixer elements having atotal of 128 binary dividing/mixing operations and a void volume of 1.88ml. This would provide a total of 2^128 or 3.4×10^38 subdivided volumeelements, having a characteristic dimension of 1.8×10^−6 nm or someseven orders of magnitude smaller than a virus. The feedstock was plasmaspiked with bacteriophage phi-X 174 to a titre of around 10^8; afterdiluting ten-fold the (original) optical density was calculated to be23.5 at 254 nm in a 1 cm cuvette. The flow rate was varied from 3.9ml/min to 18.8 ml/min giving residence times from 6 to 28 seconds. Thenumerical results are summarized in table 4 and the log kill versusresidence time figures are plotted in FIG. 5, the figures in parenthesesare the flow rates for each data point. Examination of the plot in FIG.5 shows that the minimum flow rate for efficient mixing, as judged bythe steepest part of the curve in this case was around 13 ml/min, with acorresponding slope of 0.4 3 logs kill per second of residence time.Thus doubling the length of pipe relative to example 2 has resulted indouble the flow rate (and consequently productivity) for the same amountof virus kill whilst maintaining the efficiency (slope) at 0.43logs/sec. This demonstrates that it is feasible to scale up productivityand maintain virus kill by increasing the length of illuminated mixingpipe. In contrast, reducing the rate of flow below a critical value willoffer no benefits in terms of virus kill or productivity. Furthermorethe data of table 4 show that both backpressure and temperature rise canbe maintained within acceptable limits.

EXAMPLE 4 Inactivation of Virus Using Increased Flow Rate

As for example 3 except that the flow rate used was varied in the range20 to 100 ml min, and the plasma (spiked with bacteriophage phi-X 174)had an original optical density of 24.32 at 254 nm in a 1 cm cuvette.The numerical data are summarized in table 5 and the values for logvirus kill are plotted against residence time in FIG. 6, the figures inparentheses are the flow rates at each data point. The data in table 5show that even at these high flow rates, back pressure is still wellwithin the practical limit for operating with peristaltic pumps andtubing, and the temperature rise is small. Actinometry data wereconsistent with an effective lamp power of 17 mW/cm^2.

The virus log kill data from table 5 are plotted in FIG. 6 as a functionof residence times, and show that compared to the lower flow rates inexample 3 and FIG. 5, the faster flow rates now ensure that all datapoints fall on the linear and steepest part of the curve whichcorresponds to the region of efficient mixing. Furthermore theefficiency, expressed as the slope of this line is 0.46 logs per second,thus it is maintained essentially identical to that obtained in examples2 and 3. We consider that this is a valuable attribute of working in theregion of efficient mixing, above the minimum flow rate, since it allowsfor accurate prediction of virus kill and scaling up performance byincreasing pipe length.

1. A portable micro-organism inactivation system suitable for use withindividual fluid units, comprising: a casing mounting a UV radiationsource, pump means, and releasable tube support means; and an elongatetube having: a first portion with wall means of a UV-transparentmaterial and having an internal diameter of around 3 mm, and containinga static flow mixing means extending therealong with a multiplicity ofmixer elements for repeatedly subjecting a fluid flow therethrough, inuse of the system, to a mixing operation comprising dividing andremixing of the fluid flow substantially without inducing turbulence insaid fluid flow, in use of the system; a second portion interfaced withsaid pump means for pumping of fluid therethrough by said pump means inuse of the system; upstream and downstream ends provided with first andsecond coupling means respectively for releasable fluid-tight connectionof said elongate tube, in use of the system, to an individual fluid unitcontainer of fluid to be treated and to a treated fluid container forreceiving treated fluid, respectively, and having a sterile interior,said releasable tube support means being formed and arranged forreleasably supporting said elongate tube so as to define a flow pathextending therethrough which is substantially free of substantialdiscontinuities so as to substantially avoid turbulence in fluid flowingtherealong in use of the system, and with substantially only said firstportion extending in close proximity to said UV radiation source withinan irradiation zone thereof, and with said second portion interfacedwith said pump means, said pump means being provided with a flowcontroller formed and arranged for limiting the flow of said fluidthrough said tube between predetermined flow rate limits so that in useof the system substantially the whole of said individual fluid unit isexposed to a similar micro-organism inactivating level ofUV-irradiation, whilst minimizing damage to the desired componentsthereof, and then collected in a said treated fluid container.
 2. Aportable micro-organism inactivation system suitable for use withindividual fluid units, comprising: a casing mounting a UV radiationsource, pump means, and releasable tube support means; and an elongatetube having: a first portion with wall means of a UV-transparentmaterial, and containing a static flow mixing means extending therealongwith a multiplicity of mixer elements for repeatedly subjecting a fluidflow therethrough, in use of the system, to a mixing operationcomprising dividing and remixing of the fluid flow substantially withoutinducing turbulence in said fluid flow, in use of the system; a secondportion interfaced with said pump means for pumping of fluidtherethrough by said pump means in use of the system; upstream anddownstream ends provided with first and second coupling meansrespectively for releasable fluid-tight connection of said elongatetube, in use of the system, to an individual fluid unit container offluid to be treated and to a treated fluid container for receivingtreated fluid, respectively, and having a sterile interior, saidreleasable tube support means being formed and arranged for releasablysupporting said elongate tube so as to define a flow path extendingtherethrough which is substantially free of substantial discontinuitiesso as to substantially avoid turbulence in fluid flowing therealong inuse of the system, and with substantially only said first portionextending in close proximity to said UV radiation source within anirradiation zone thereof, and with said second portion interfaced withsaid pump means, said pump means being provided with a flow controllerformed and arranged for limiting the flow of said fluid through saidtube between predetermined flow rate limits so that in use of the systemsubstantially the whole of said individual fluid unit is exposed to asimilar micro-organism inactivating level of UV-irradiation, whilstminimizing damage to the desired components thereof, and then collectedin a said treated fluid container, wherein said static flow mixing meanscomprises a series of 3 mm diameter static helical mixer moldings andsaid first portion of said elongate tube is made of heat shrinkable PTFEtubing which has been shrunk to have an internal diameter of 3.0 mm. 3.A portable micro-organism inactivation system suitable for use withindividual fluid units, comprising: a casing mounting a UV radiationsource, pump means, and releasable tube support means; and an elongatetube having: a first portion with wall means of a UV-transparentmaterial, and containing a static flow mixing means extending therealongwith a multiplicity of mixer elements for repeatedly subjecting a fluidflow therethrough, in use of the system, to a mixing operationcomprising dividing and remixing of the fluid flow substantially withoutinducing turbulence in said fluid flow, in use of the system; a secondportion interfaced with said pump means for pumping of fluidtherethrough by said pump means in use of the system; upstream anddownstream ends provided with first and second coupling meansrespectively for releasable fluid-tight connection of said elongatetube, in use of the system, to an individual fluid unit container offluid to be treated and to a treated fluid container for receivingtreated fluid, respectively, and having a sterile interior, saidreleasable tube support means being formed and arranged for releasablysupporting said elongate tube so as to define a flow path extendingtherethrough which is substantially free of substantial discontinuitiesso as to substantially avoid turbulence in fluid flowing therealong inuse of the system, and with substantially only said first portionextending in close proximity to said UV radiation source within anirradiation zone thereof, and with said second portion interfaced withsaid pump means, said pump means being provided with a flow controllerformed and arranged for limiting the flow of said fluid through saidtube between predetermined flow rate limits so that in use of the systemsubstantially the whole of said individual fluid unit is exposed to asimilar micro-organism inactivating level of UV-irradiation, whilstminimizing damage to the desired components thereof, and then collectedin a said treated fluid container, wherein said first portion has aninternal diameter of from 1 mm to around 3 mm.
 4. A system as claimed inclaim 3, wherein the system has a void volume of from 1 to 10 ml.
 5. Asystem as claimed in claim 3, wherein the pump comprises a pump motorand drive transmission components which are isolated from the fluid tobe treated.
 6. A system as claimed in claim 3, wherein said pumpcomprises an impeller disposed within said elongate tube, and drivemeans formed and arranged for driving said impeller within the elongatetube to pump, wherein the drive means is disposed externally of theelongate tube.
 7. A system as claimed in claim 5 wherein said pump is adiaphragm pump in which the second portion of the tube is connected viaone-way inlet and outlet valves to a chamber having a diaphragm wallportion which is reciprocally displaceable by a pump motor andreciprocating drive output member inter-engaged with the outside of thediaphragm wall.
 8. A system as claimed in claim 5 wherein said pump is aperistaltic pump.
 9. A system as claimed in claim 3, wherein the pumpmeans is formed and arranged so as to provide a fluid flow rate of notless than a minimum flow rate corresponding to a maximum fluid residencetime within said irradiation area required for efficient mixing asindicated by the maintenance of a substantially linear relation betweenlog₁₀ kill and residence time which is obtained above said minimum flowrate and at a fluid flow rate not greater than a maximum fluid flow ratecorresponding to a minimum residence time in said irradiation arearequired for effective inactivation of a said contaminatingmicro-organism by providing a desired log₁₀ kill of said micro-organism,wherein said minimum residence time in said irradiation area is definedin accordance with the following relationship in which:${{\log_{10}\mspace{11mu}{kill}} = \frac{K \times {Flux} \times {Residence}\mspace{14mu}{time}}{{OD} \times {Tube}\mspace{14mu}{Radius}}},$wherein: Flux indicates the amount of UV radiation incident on thepassage containing the fluid flow in the irradiation area, in mW·cm⁻²;OD is the Optical Density of the fluid at the wavelength in the regionwhere substantial virus inactivation takes place; K is an empiricallyderived constant; and Tube Radius is the internal radius of the vesselin the irradiation area, in centimetres, whereby in use of the systemsubstantially the whole of the fluid may be exposed to a similarmicro-organism inactivating level of UV-irradiation whilst minimisingdamage to the desired component(s) of the fluid.
 10. A system as claimedin claim 9 wherein the pump means is formed and arranged to provide afluid flow rate not greater than a fluid flow rate which provides alog₁₀ kill of
 4. 11. A system as claimed in claim 3, wherein theelongate tube is formed from discrete sections forming said first andsecond portions, and one or more connector sections disposedtherebetween which, in use, interconnect said first and second portionsto each other to allow a said fluid flow therethrough.
 12. A system asclaimed in claim 11 wherein one or more of said one or more connectorsections are formed from a flexible material.
 13. A system as claimed inclaim 3, wherein the static flow mixing means comprises an elongatescrew threaded member formed from alternate helical mixer elements ofopposite handed screw thread.
 14. A system as claimed in claim 3,wherein the first portion of the tube is formed from a material having aUV-transmissibility of at least 50% at about 254 nm.
 15. A system asclaimed in claim 3, wherein more than one length of said elongate tubeis disposed in the irradiation zone adjacent the UV-radiation sourcelamp so that the first portion comprises a plurality of lengths ofsubstantially UV transparent tubing containing static mixer elements,which lengths are inter-connected in series by connecting sections. 16.A system as claimed in claim 3, wherein said system is powered by aportable power source selected from one or more of the group consistingof at least one battery, at least one rechargeable battery, at least onesolar cell, and a manually driven dynamo.
 17. A system as claimed inclaim 3, wherein the pump means is formed and arranged to provide atleast one fluid flow rate in the range from 2 ml/min to 100 ml/min. 18.A system as claimed in claim 3, wherein said first portion is made ofheat shrinkable tubing which has been shrunk to have an internaldiameter equal to the diameter of said static flow mixing means.